If your truck is pre-2012 GMC, it requires your dealer to activate the trailer connector's 12V power. Of course, you can do it yourself, but I can't remember the fuse box circuit number. Probably on the Internet if you search.
Mike & Pam '12 36RL, Kodiak Discs, 17.5" G114s H-Rated, SRE4000 w/HD Shackles, Joy Rider Shocks, Flex Air, 5.5 Onan, W&D, DW, 4 Scare Lights, (2) 6V Trojan T-145s; Progressive EMS-HW50C, Winegard DTV Sat, Sony/Denon 4K Home Theater, WiFiRanger EliteAC Pack, weBoost 4G-X Cell Booster.
2020 RAM 3500 Limited CC, LB, 4x4, DRW, Max Tow, Cummins HO, AISIN, 4.10, Mopar 30K w/OEM Prep, Transfer Flow 70gal Aux Tank/Toolbox.